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Anaphylaxis: a dangerous allergic reaction

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Anaphylaxis, also known as anaphylactic shock, is an extreme allergic reaction that can be life-threatening. Anyone experiencing anaphylaxis should receive immediate medical attention.

What can cause anaphylaxis?

The common triggers of anaphylaxis, known as allergens, in susceptible people are:

Foods, particularly nuts, shellfish and dairy products

Drugs, commonly penicillin

Stings of wasps or bees

Anaphylaxis can also be triggered by contact with products that contain latex, such as latex gloves.

Anaphylaxis occurs when one of the allergens, listed above, enters the body causing the bodies’ special ‘mast cells’ to produce and release an enzyme called tryptase. These levels should be measured with a blood test immediately and also tow to four hours later to confirm anaphylaxis occurred in accordance with the guidelines set out by NICE (the National Institute for Health and Clinical Excellence).

How common is anaphylaxis?

The true incidence of anaphylaxis is not known but the Department of Health states 3,000 people are admitted into hospital with anaphylaxis per year, a threefold increase in recent years. There are approximately 20 anaphylaxis deaths per year in the UK according to a report by the Resus Council in 2008. Many of these deaths are preventable. Approximately 1 in 12 people who have one anaphylactic reaction will have another one at some time in the future.

The first episode of anaphylaxis is often a medical emergency involving treatment by paramedics. Once identified as being at risk, you need to take steps to protect yourself:

You must avoid the substance you are allergic to as far as possible.

You need to carry an adrenaline auto-injector (e.g. EpiPen ®) to treat yourself immediately if you are exposed unexpectedly to the triggering allergen.

What are the symptoms of anaphylaxis?

The symptoms of anaphylaxis are caused by the release of large amounts of histamine and other chemicals into the bloodstream. Histamine causes blood vessels to dilate, which causes a sudden drop in blood pressure. Excess histamine may also cause blood vessels to leak, releasing fluid into the tissues and causing a further fall in blood pressure. Low blood pressure may make you feel light-headed at first but it can lead rapidly to collapse. Histamine also causes narrowing of the breathing tubes leading to difficulty in breathing. The heart rate can become fast and erratic.

Other symptoms of anaphylaxis include:

Itchiness: this may be accompanied by urticaria, commonly known as nettle rash, or hives

Angioedema: this is rapid swelling of the skin, subcutaneous tissue, and mucous membranes, particularly around the eyes, lips, genitals and anus. It may be accompanied by soreness. Hands and feet may also be swollen.

Gastric problems: these include nausea, vomiting, diarrhoea, abdominal cramps and a metallic taste in the mouth.

Fright: true anaphylaxis may mean you experience severe anxiety and a feeling of doom. It is also common to feel feverish and sweaty.

What to do if someone is in anaphylactic shock

Any case of anaphylaxis, even if mild at first, should be viewed as a medical emergency. So, if you are with someone who goes into anaphylactic shock, you should immediately call for a paramedic ambulance.

While waiting for the ambulance, your priority is to make sure that the affected person can breathe, so check the affected person’s pulse and breathing. If the anaphylaxis is induced by a bee sting, remove the sting as quickly as possible. In addition:

If the affected person is conscious: make sure the person is flat with their legs raised. Loosen clothing.

If the affected person is unconscious: lean the head back. Place one arm under the chin to further raise the head. Again, loosen clothing. Make sure that their head lies to the side; this is to ensure that vomiting, if it occurs, does not cause choking.

If the affected person stops breathing or his or her heart stops: perform cardiopulmonary resuscitation. This involves placing the hands in the centre of the chest and compressing to a depth of about 5cm at a rate of 2 per second. You may also perform mouth-to-mouth ventilation but this should not be done at the expense of the chest compressions.